Non-metallic liquid-tight (NMLT) type I conduit is a form of electrical conduit which has been developed for use in locations where liquid will be present and, in many cases, where electrical conductors must extend between two locations which are expected to move relative to each other. Examples of environments of this type will be found in many machine tools in which an electrically driven or adjusted tool is mounted in a cutting head which repeatedly swings or reciprocates relative to the machine base, and in which a cutting or coolant fluid is sprayed, squirted or flowed around the tool. In order to get power to the moving head, some sort of liquid-resistant conduit must be used, and the conduit is preferably flexible to accommodate the motion.
NMLT type I conduit is, essentially, a rubber tube having inner and outer plies with a woven fiber layer between the two plies. It is produced by several manufacturers to different specifications which, unfortunately, results in considerable variation in the inner and outer diameters, wall thickness and material consistency.
It will be apparent that an MNLT conduit is of little value unless connector fittings can be provided to couple the ends of such conduit to housings or through walls. Such fittings should be easy and quick to assemble on the conduit but, once assembled, they must be liquid-tight and must engage the conduit with sufficient force to withstand a 150 pound pull test prescribed by Underwriters Laboratories, Inc.
In order for the fitting to be easy to assemble, there must be sufficient clearance between the components and conduit to allow the parts to be slipped together but, once assembled, the parts must obviously engage the conduit tightly without "wrinkling" the end of the conduit because such wrinkles can defeat the liquid-tight integrity of the connector.